Based on my experience with the M103, high oil consumpion is usually due to worn valve stem seals. The seals can be replaced rather easily and inexpensively without removing the head. Also, the rapping noise on start up might be due to a faulty check valve that is at the base of the oil filter housing. I saw a post on this subject a while back. Apparently, the valve prevents oil from draining out of the upper engine when it is shut off. If the check valve leaks, you will get a clattering noise for a few seconds on startup until the oil makes its way back up there.
Just thought I would inform you of these things before you decided to get the complete head rebuilt.